The invention relates to an apparatus for moving an operating element within a cavity surrounded by a guide surface, the operating element being used for example to open a vessel containing gas used to inflate a vehicle airbag.
An apparatus of the type disclosed herein is used in the movement of structural parts that are used for opening or closing or for adjusting cross-sections of a flow path, for example the flow path of a gas. Normally, the operating element is driven in a pulsed manner in dependence on a sensor signal, in which case the required operating movement or actuation movement caused by the operating element is to be triggered within a short time, in the order of magnitude of a few milliseconds. Mechanisms of this type are used for example for opening vessels containing gas used to inflate airbags. The movement mechanism used in this very rapid operation necessitates a high degree of precision as regards the dimensions of the operating element and the guide surface, with at the same time a large number of components. Furthermore, when the structural parts to be moved by the operating element, such as flap valves, supports and the like, are impacted by the operating element high reaction forces are generated. Problem-free guidance of the operating element within the cavity enclosed by the guide surface must be guaranteed during the rapid movement of the operating element without tilting moments or the like having a disadvantageous effect on this guided movement. Preferably, a pyrotechnic drive is used as the drive means generating the driving pulse.
There is provided in accordance with the present invention an apparatus for moving an operating element along a guide surface surrounding the operating element. A drive means provides a driving pulse exerted on the operating element for the movement of the operating element along the guide surface. A gap between the guide surface and the outer surface of the operating element is filled by a layer of a material that acts as an adhesive layer when the operating element is at rest and as a lubricating layer when the operating element is in motion. The outside of the operating element may have a conical profile, with the gap between the guide surface and the outer surface of the operating element becoming progressively larger in the direction of movement of the operating element. The layer of material in the gap may be a dry or solid lubricant, such as MoS2 or polytetrafluoroethylene.